The question asks what is important to do when encountering an aggressive driver. Let's evaluate the options: a) remain calm*: This is the recommended and safest approach. Staying calm helps you make rational decisions, avoid escalating the situation, and maintain control of your vehicle. b) get aggressive*: Responding with aggression will only worsen the situation, increase the risk of a confrontation, and make the road more dangerous for everyone. c) speed up*: Speeding up to get away from an aggressive driver can lead to reckless driving, increase your own risk of an accident, and might even provoke the aggressive driver further. It's generally better to create distance safely, which might involve slowing down or changing lanes, rather than speeding. Therefore, remaining calm is the most appropriate and safest action. The correct option is a). $$\boxed{\text{a) remain calm}}$$